Technical Field of the Invention: A structural member required to have a prescribed strength in an aircraft, an automobile, a vessel or a constructed structure, etc., especially in a circular bore portion or a curved portion such as a wing or a body of an aircraft. Technical Problem: A preform for a fiber-reinforced composite material to be used as a structural member of a fiber-reinforced composite material having a curved portion is to be manufactured through a low-cost mass production. Means of Solving the Problem
A preform for a fiber-reinforced composite material (20) including a bent portion (22) along a curved line for bending (12), a flange portion (24) corresponding to an outer circumferential portion (14) and a semi-cylindrical portion (26) formed by bending an inner circumferential portion (16), based on a precursor of a preform for a fiber-reinforced composite material (10) provided with the curved line for bending (12) located in a flat plane or a curved plane region having a predetermined extension; the outer circumferential portion (14) corresponding to a region (a) where a plurality of reinforced fibers is partly disposed in parallel along the curved line for bending (12), and the inner circumferential portion (16) corresponding to the section (b) constituted solely of another plurality of reinforced fibers disposed throughout the entire area, so as to intersect the former plurality of reinforced fibers at a predetermined angle in the region (a). Principal Use: An aircraft, an automobile, a vessel, a constructed structure, etc. Especially a window frame or a fuel inlet of an aircraft.